Synthesis and construction of aggregation induced emission based sensor for colorimetric multiphase sequential sensing of Al3+ and CN− with real sample applications: Development of efficient vapor phase pH sensor

Abstract

A sensitive and optically selective 4-phenoxyphenyldiazenyl-biphenyl-2-ol sensor PDP exhibited photo-switchable behavior, excellent solvatochromic nature, large Stoke’s shift (172 nm), aggregation induced emission (AIE) and colorimetric characteristics. The sensor PDP (PDP = 20 µM, λ_absorption = 323 nm, λ_emission = 495 nm) with such amazing photophysical properties was employed for sequential sensing of Al³⁺ and CN⁻ through OFF-ON-OFF fluorescence emission approach. The sensing selectivity of sensor PDP is greatly dependent on diazo cavity and hydroxy functionality in PDP molecule. Azo dye-based PDP sensor has been simply synthesized through quick and economical diazotization coupling synthetic approach and characterized through spectroscopic techniques. Sensor PDP exhibited AIE nature with a slight blue shift from 20 to 90 % water fraction that demonstrates the formation of H-aggregates. The size of aggregates was investigated through DLS analysis. The quantified minimum detection limit (LOD) of sensor PDP for Al³⁺ and CN⁻ are 35 nM and 45 nM, respectively. UV Vis., fluorescence, DLS, NMR and LRMS titration were executed to investigate the interaction between PDP and Al³⁺. The sensor PDP was used for real time sequential detection of Al³⁺ and CN⁻ in food materials. Due to the excellent colorimetric feature of sensor PDP, a paper or TLC-based strip was fabricated and utilized for on-site solid-state colorimetric sensing of Al³⁺ and CN⁻. Interestingly, PDP sensor is also sensitive toward strong acid-base pH in both solution and solid phase, and it is further developed for vapor phase sensing of TFA. Finally, the logic gate is fabricated for real time monitoring of analytes. Furthermore, all these experimental findings were validated through detailed DFT studies.